双向链表的建立

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>

typedef struct my_test {
	int data;
	struct my_test *prev;
	struct my_test *next;
} T;

T *head = NULL;
//双向链表
int add1(T *head, T *node)
{
	if (!head->next) {
		node->next = head->next;
		node->prev = head;
		head->next = node;
		return (0);
	}
	node->prev = head;
	node->next = head->next;
	head->next->prev = node;
	head->next = node;

	return (0);
}
//双向循环链表
int add(T *head, T *node)
{
	if (!head->next) {
		node->next = head;
		node->prev = head;
		head->next = node;
		head->prev = node;
		return (0);
	}
	node->prev = head;
	node->next = head->next;
	head->next->prev = node;
	head->next = node;
	return (0);
}

void print(T *head)
{
	T *tmp = head;
	while (tmp) {
		sleep(1);
		printf("%d\n", tmp->data);
		tmp = tmp->prev;
	}
}

int main(void)
{
	int i = 0;
	head = (T *)malloc(sizeof(T));
	if (NULL == head) {
	  perror("malloc");
	  exit(EXIT_FAILURE);
	}
	head->next = NULL;
	head->prev = NULL;
	head->data = 10;
	for (i = 0; i < 10; i++) {
		T *node = (T *)malloc(sizeof(T));
		if (NULL == node) {
			perror("malloc");
			exit(EXIT_FAILURE);
		}
		node->next = NULL;
		node->prev = NULL;
		node->data = i;
		add(head, node);
	}
	print(head);

	return (0);
}